[PATCH] D53241: [GlobalOpt] Never remove global values from non-discardable COMDATs

[Aaron Hill via Phabricator via llvm-commits]

Aaron1011 created this revision.
Aaron1011 added reviewers: pcc, tejohnson.
Herald added a subscriber: llvm-commits.

Currently, GlobalOpt will remove global values from non-discardable COMDATS (COMDATS which have at least one live object) if the value in question has local linkage.
As described in https://reviews.llvm.org/D53234, this is an invalid treatment of COMDAT members, and can lead to issues when using MD_Associated metadata.

I've modified GlobalOpt to always bail out of global value removal if the global value is in a non-discardable COMDAT.
I've also modified the associated test to check that one of its functions, which GlobalOpt currently removes due to its local linkage, is now kept.


Repository:
  rL LLVM

https://reviews.llvm.org/D53241

Files:
  lib/Transforms/IPO/GlobalOpt.cpp
  test/Transforms/GlobalOpt/preserve-comdats.ll


Index: test/Transforms/GlobalOpt/preserve-comdats.ll
===================================================================
--- test/Transforms/GlobalOpt/preserve-comdats.ll
+++ test/Transforms/GlobalOpt/preserve-comdats.ll
@@ -24,7 +24,7 @@
   store i8 42, i8* @simple_global
   ret void
 }
-; CHECK-NOT: @init_simple_global()
+; CHECK: define internal fastcc void @init_simple_global() unnamed_addr comdat($comdat_global)
 
 define i8* @use_simple() {
   ret i8* @simple_global
Index: lib/Transforms/IPO/GlobalOpt.cpp
===================================================================
--- lib/Transforms/IPO/GlobalOpt.cpp
+++ lib/Transforms/IPO/GlobalOpt.cpp
@@ -1743,7 +1743,7 @@
     return false;
 
   if (const Comdat *C = GV.getComdat())
-    if (!GV.hasLocalLinkage() && NotDiscardableComdats.count(C))
+    if (NotDiscardableComdats.count(C))
       return false;
 
   bool Dead;


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